"Senate Judiciary Committee staffers plan to take a look at allegations that Microsoft has made it difficult for competing Web browsers to run on a certain version of Windows, an aide to Antitrust subcommittee Chairman Herb Kohl told The Hill Thursday." Good. We have to nip this in the bud, and with a bit of luck, it alerts Washington to the iOS situation as well. More browser competition equals a better web - mobile devices aren't magically exempt from this just because they have no keyboard. As simple as that.

On the other hand it is a rather bad idea to in law enforce that all operating systems has to provide arbitrary applications with simultaneously writable and executable memory. There is certainly a huge security advantage to banning it.

They don't provide the CLR compiler to metro apps on ARM as well.
That could be a middle ground: let Firefox et al compile Javascript to CLR, then let Microsoft's own JIT take care of security and speed.

It's allowed to use the JIT on x86, but not on ARM. It's all about iOS-style lock-in (you can't easily run downloadable code that way).

iOS was an oversight (who would have thought that Apple creates a hit?), but Microsoft is usually market leader by "Version 3".

The iOS lock-in should be fixed, the Metro lock-in avoided. No need to repeat making mistakes.